The present invention relates to the laser apparatus and a method of making the laser apparatus and especially to a gas Waveguide laser apparatus having hard sealed optical to metal seals and temperature compensation.
In the past, a wide variety of gas lasers have been provided. Many of these are CO.sub.2 Waveguide lasers which fall within the same classification as the present laser apparatus. Typically, a Waveguide laser has a wave guide which may be made of a ceramic material having a bore extending therethrough and filled with a gas such as CO.sub.2. Electrodes are placed adjacent to a wave guide tube for pumping the gas located in the Waveguide tube. Each end of the tube generally has a mirror mounted thereto, one of them with substantially total reflection and the other mirror having a partial reflecting surface to allow the escape of laser energy.
The present invention is directed towards a wave guide laser as well as to a method of making a wave guide laser, utilizing a ceramic Waveguide but having a circulating gas ballast tank and electric pump to circulate the CO.sub.2 gas from the ballast tank through the wave guide bore, and includes special optical assemblies and temperature compensating design, as well as a method of making a laser apparatus in accordance with the invention.
Prior art lasers can be seen in the Newman Waveguide Laser U.S. Pat. No. 4,381,564, having a capacitively of coupled discharge which includes a wave guide having a bore therethrough, along with a pair of high voltage electrodes driven by high voltage supply. An optical assembly is mounted to each end of the wave guide for mounting mirrors at each end of the bore of the Waveguide. A tube connects each end of the wave guide assembly to connect a gas reservoir and a circulator to allow the gas within the bore to be replenished and recirculated. The Noble et al., U.S. Pat. No. 4,065,370 is for the ion plating of a thin metallic strip to a flashlamp for triggering the flashlamp. Prior art seals or mounting for optics can be seen in the prior Holtz U.S. Pat. No. 3,599,112 and in the Knowles U.S. Pat. No. 3,978,425. In the Ljung et al. U.S. Pat. No. 4,153,317, an indium seal for gas lasers is illustrated. Indium is a common prior art technique for attaching laser optics to optical assemblies, while another common prior art uses an epoxy adhesive to attach the laser mirror to the laser assembly. The Ljung Patent also suggests the passive alignment of the optics prior to the mounting and the sealing of the optics by optical contact, epoxy, or glass frit, then evacuating and filling the laser. Fine alignment is accomplished in this laser by deforming the support of one or both mirrors by using a metal tube with a neck-down section using set screws to accomplish the adjustment. Other glass to metal seals can be seen in the Knowles U.S. Pat. No. 3,978,425 for laser components and fabrication methods. This patent has a metal casing in which the optical elements are attached to a kovar gridwork and has interconnected annular portions placed in a mold and optical glass pellets introduced onto each ring so that the application of heat melts the glass and forms the glass directly onto the kovar rings. Alignment of the optical elements is by displacing the metal casing slightly. In U.S. Pat. No. 4,393,506 to Laakmann at al., a method is disclosed for manufacturing a sealed-off RF excited CO.sub.2 laser with a longer operating life. The present invention is also directed towards a wave guide laser which has a longer shelf and operating life. A number of factors have been identified as the principle causes of limiting the operating life of a sealed-off CO.sub.2 laser. Sealed-off lasers are utilized because they do not require auxiliary gas cylinders and vacuum pumps and so that they can be more readily portable. However, one of the problems associated with sealed-off CO.sub.2 lasers is that of maintaining stable long-term operation despite factors which tend to destabilize the gas chemistry, such as CO.sub.2 disassociation.
There are a large number of prior art patents which deal with either temperature compensation for maintaining the alignment of the optics or with specific alignment techniques for the optics. Typical prior art patents of this nature can be seen in the Singleton U.S. Pat. No. 4,342,117; Marlett et al., U.S. Pat. No. 4,224,579; the Smars U.S. Pat. No. 3,671,883; Sepp et al., U.S. Pat. No. 4,457,001; the Hamerdinger et al., U.S. Pat. No. 4,149,779 and in the Barnaby U.S. Pat. No. 3,605,036. The Singleton Patent teaches a mirror mounting arrangement for a gas laser which connects the mirror optics to a flanged cup which is then connected to another flanged cup attached to the body using an annular spacer member between the flanged cups and a sealing technique that does not require epoxy resin or indium seals.
In contrast to the prior art, the present invention provides for a Waveguide assembly having a gas ballast tank and a permanent magnet circulating pump for circulating the CO.sub.2 through a ceramic wave guide and has alignment rods selected and supporting the optical assemblies on each end of the Waveguide to match the temperature expansion of the wave guide while allowing the alignment of the optical mirrors. The optical mirrors are mounted to an expansion tube expanding in the opposite direction from the wave guide and alignment bars and is selected to negate the expansion of the Waveguide and alignment rods to maintain the laser mirrors in alignment. The method of making the laser allows for a window blank to be inserted into a window ring and attached with a glass frit seal at 400 degrees centigrade in nitrogen and to attach this to the optical assemblies. The optical assemblies can then be baked at a high temperature for long periods of time for removing moisture and impurities therefrom prior to filling with the CO.sub.2 gas.